Material Defects in Superconducting Quantum Computers | Seminar Series with Jürgen Lisenfeld

Material Defects in Superconducting Quantum Computers Your formal invite to weekly Qiskit videos ► https://ibm.biz/q-subscribe Speaker: Dr. Jürgen Lisenfeld Physikalisches Institut, Karlsruher Institut für Technologie (KIT), Karlsruhe Host: Zlatko Minev, PhD. Abstract: Superconducting quantum bits have reached a pole position in the race to realize a quantum computer. Yet, the coherence of such solid-state qubits is severely limited by defects in the circuit materials. These provide a bath of parasitic two-state quantum systems, so-called TLS, which give rise to fluctuations and dissipation of qubit energy. Understanding the microscopic origins of TLS defects and learning how to avoid them will be vital for progressing towards practical quantum computers. I will review our experiments where we operate superconducting qubits as sensitive detectors to study individual TLS defects. We can manipulate the defects' quantum states by resonant microwave driving and read them out by coherent swap operations. Moreover, tuning of TLS by applied mechanical strain and tailored electric fields provides novel spectroscopy methods that reveal mutual defect interactions and allow one to determine the defects' locations in a given qubit sample. These techniques provide new insights into disordered materials and yield valuable information to guide improvements in sample fabrication that are urgently needed to obtain higher coherence in micro-fabricated quantum devices. Bio: Dr. Jürgen Lisenfeld 2003 - Diploma (equal to Master) in Physics titled "Probing Quantum States in Josephson Junctions by Microwaves" in the group of Prof. Alexey Ustinov at University of Erlangen, Germany. 2007 - PhD in Physics with thesis "Experiments on superconducting Josephson phase quantum bits", also in the Ustinov group. My work included the first demonstration of coherently operated superconducting qubits in Germany by the year 2005. 2008 - 2009 PostDoc at Karlsruhe Institute of Physics in Karlsruhe, Germany. Transfer of Ustinov group to Karlsruhe and set up of new qubit laboratories. 2010 PostDoc in the group of Prof. Hans Mooij at TU Delft, Netherlands. Research on Flux qubits developing methods for two-qubit gates and the study of ultra-strong qubit-resonator coupling. 2011 - 2022 PostDoc back at KIT Karlsruhe. Focus on the study of material defects in superconducting phase and transmon qubits. Research Highlights: Pioneered ultrastrong coupling of a resonator to a flux qubit. P. Forn-Díaz, J. Lisenfeld, D. Marcos, J.J. Garcia-Ripoll, E. Solano, CJPM Harmans, and J.E. Mooij., PRL 105, 237001 (2010) Developed strain-tuning of material defects detected by a qubit. G.J. Grabovskij, T. Peichl, J. Lisenfeld, G. Weiss, A.V. Ustinov, Science 338, 232 (2012) First observation of interacting TLS defects in a Josephson junction. J. Lisenfeld, G.J. Grabovskij, C. Müller, J.H. Cole, G. Weiss, and A.V. Ustinov, Nat. comm. 6, 6182 (2015) Using individual, coherently controlled TLS defects as quantum spectrum analyzers to study their environment. J. Lisenfeld, A. Bilmes, S. Matityahu, S. Zanker, M. Marthaler, M. Schechter, Scientific Reports 6, 23786 (2016) Electric-field tuning of individual TLS defects in transmon qubits. J. Lisenfeld, A. Bilmes, A. Megrant, R. Barends, J. Kelly, P. Klimov, G. Weiss, J.M. Martinis, and A.V. Ustinov, npj Quant. Inf. 5, 1 (2019) -- The Qiskit Seminar Series is a deep dive into various academic and research topics within the quantum community. It will feature community members and leaders every Friday, 12 PM EDT.